Add some missing tests on text field

[corranwebster]

Forgot tests for a couple of attributes.

[jwiggins]

This is good? The tests you added failed. TDD!

[corranwebster]

The code was written on a computer where I couldn't easily do testing (didn't particularly want to install EDM on it). But it is good that it failed, as it looks like there may be an actual bug or two.

[corranwebster]

Test cases hopefully now working on all platforms. This is why we write tests.

[codecov-io]

Codecov Report

Merging #368 into master will increase coverage by 0.02%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #368      +/-   ##
==========================================
+ Coverage   36.31%   36.33%   +0.02%     
==========================================
  Files         481      481              
  Lines       26398    26398              
  Branches     3909     3909              
==========================================
+ Hits         9586     9592       +6     
+ Misses      16399    16391       -8     
- Partials      413      415       +2

Impacted Files	Coverage Δ
pyface/fields/i_text_field.py	73.91% <100%> (+2.89%)	⬆️
pyface/ui/wx/fields/text_field.py	86.04% <100%> (+4.65%)	⬆️
pyface/ui/qt4/fields/text_field.py	88.09% <100%> (+4.76%)	⬆️

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[jwiggins]

👍 once the print is gone